1. Field of the Invention
The present application relates generally to thermoelectric materials, and more specifically to thermoelectric materials having porosity.
2. Description of the Related Art
Thermoelectric (TE) materials can be used in power generation mode by converting heat into electrical power directly, or can be used in cooling (Peltier) mode by converting a voltage difference into a temperature difference. TE coolers and generators are solid-state motionless devices, and thus extremely compact and reliable. Doubling their efficiency may pave the way for their widespread use in waste heat recovery and refrigeration (L. Bell, “Cooling, heating, generating power, and recovering waste heat with thermoelectric systems,” Science, Vol. 321, 1457-1461 (September 2008)). TE technology then promises to contribute significantly to world-scale energy conservation efforts.
The device efficiency is determined primarily by the thermoelectric figure of merit zT of the TE materials of the device. The value of zT is currently about 1 in commercial materials and has reached 1.5 and greater using nano-structuring to reduce the thermal conductivity (M. Kanatzidis, “Nanostructured thermoelectrics: the new paradigm?” Chem. Mater. Vol. 22, 648-659 (2010)), and band structure engineering (G. D. Mahan, “Good Thermoelectrics” in Solid State Physics (eds. H. Ehrenreich and F. Spaepen) Vol. 51, 81-157 (Academic, NY, 1998)) such as the use of resonant impurity levels (J. Heremans, V. Jovovic, E. Toberer, A. Saramat, K. Kurosaki, A. Charoenphakdee, S. Yamanaka, and G. Synder, “Enhancement of thermoelectric efficiency in PbTe by distortion of the electronic density of states,” Science Vol. 321, 554-557 (July 2008)) to increase the thermoelectric power.